Patent GB-500971-A (GB)
Title: Improvements in arrangements for limiting the calling possibilities of impulse transmitters in automatic telephone exchange systems
IPC: H04M1/677
Filed: 1937-08-19
Abstract: 500,971. Impulse transmitters. MARTI, F. Aug. 19, 1937, No. 22774. Convention date, Aug. 19, 1936. [Class 40 (iv)] Relates to devices associated with a dial transmitter for preventing the transmission of predetermined multidigit numbers by short-circuiting the impulse springs which may also be short-circuited by an additional keycontrolled contact to prevent unauthorized use. A relay operated ovor the short-circuit may give a signal. The shaft 11 of the transmitter has a gear wheel 14 driving a wheel 24 on shaft 25 carrying the digit discriminator 27, and wheel 14 carries a pawl 28 engaging ratchet 32 carried by the shaft 33 of a control member 35 which is thus advanced one step each time the dial is set. The contacts C<SP>2</SP> shunted across the impulse contacts are controlled by a lever 39 normally held by lever 48 against action of a spring 43 and carrying rollers 41, 42 engaging the digit discriminator 27 and control member 35 respectively. On setting the dial for the first digit, member 36 takes up the position in which a gap in the outer rib comes opposite roller 42 and discriminator 27 rotates clockwise together with a notched disc 26 which rides past a pawl 52 on lever 51 and on completion of the setting engages a notch in the disc. When the dial, discriminator 27 and disc 26 return, the first operation consists of quick action by pawl 52 on lever 51 whereby lever 48 is released from a toothed segment 46 on lever 39. If the digit is one of prohibited number, a gap in the outer rib of the discriminator presents itself to the roller 41 and as member 35 also presents a gap to roller 42 and lever 48 has been withdrawn from segment 46, lever 39 moves counterclockwise tending to close the shunt over C<SP>3</SP>. Similar operations ensue for the second and third digits, the members 27 and 35 being formed with concentric gapped ribs for this purpose. If counterclockwise movement of lever 39 occurs on all three digits, contacts C' close before the third digit is transmitted. As shown, numbers between 354 and 359 are prohibited. When the receiver is replaced on hook F, the holding pawl 38 of ratchet wheel 32 is tripped by arm 68, and arm 69 disengages holding lever 48 from segment 46, so that member 35 rotates counterclockwise to normal, the lever 39 being rotated back to normal by inclines at the ends of the ribs on 35 since aligned gaps in the ribs of discriminator 27 give freedom of movement for roller 41. Preventing fraud. The first two digits 35 could be transmitted for example by setting the dial for 8 and stopping it temporarily after 3 impulses had been transmitted. To prevent this, contacts C<SP>2</SP> normally short-circuiting the impulse contacts are provided. When ratchet wheel 32 takes its first step on setting the dial, movement of the holding pawl 38 removes the short-circuit by raising spring 59 which is held by tooth 60 on lever 62. When the dial returns normally, the end thrust of the speed regulator spindle 16 moves lever 62 clockwise and tooth 61 still holds spring 59 to prevent a shortcircuit at C<SP>2</SP>. If however the dial is temporarily stopped during the return, the second movement of the dial and lever 62 releases spring 59 to close the short-circuit. Modifications. In one arrangement, Fig. 3 (not shown), the roller 42 is carried by a separate lever and causes the shunt springs C<SP>8</SP> to close each time the dial is set, but the lever 39 when it drops through a gap in a rib opens springs C<SP>3</SP> again. In this case, the gaps in the ribs of the discriminator correspond to digits which are allowable. The shafts 25, 33 may carry additional sets of discriminating arrangements similar to members 27, 35 and lever 39.